What is the direct cause of fatigue and lack of energy due to insufficient insulin production?

The direct cause of fatigue and lack of energy due to insufficient insulin production is that body cells do not absorb glucose. Insulin is a hormone produced by the pancreas that facilitates the transport of glucose from the bloodstream into the cells, where it is used as a primary source of energy. When insulin production is insufficient, as seen in conditions like Type 1 diabetes, glucose cannot effectively enter the cells.

As a result, even though glucose may be present in the blood, cells are unable to access it for energy. This lack of energy within the cells leads to feelings of fatigue and lethargy. In contrast, the other options describe different physiological processes that do not directly impact energy levels in the same way. For example, while blood sugar levels may fluctuate, it is the inability of cells to absorb glucose that directly results in energy deficits.